I had to mail in my taxes on 3/29. But when I try to track my refund, it says there are no taxes on file. Does it usually take longer than 2 weeks by mail?

The IRS tax refund website states - Expect extended delays if you mailed your return or responded to an IRS Notice - https://www.irs.gov/refunds

Yes it can.  In normal times, it is at least 4 weeks.  But this year is far from normal.  In fact, folks who efiled more than 2 months ago are still waiting.   Per the IRS:

Expect extended delays if you mailed your return or responded to an IRS Notice

COVID-19 Mail Processing Delays

It’s taking us longer to process mailed documents including:

• Paper tax returns, and
• All tax return related correspondence.

We are processing all mail in the order we received it.

Do not file a second tax return or call the IRS.

Refunds | Internal Revenue Service (irs.gov)